Bremsstrahlung X-rays Energy Limit

For an x-ray tube at constant voltage I know that the maximum energy Bremsstrahlung x-ray that can be produced is directly related to the voltage on the tube. But what about the minimum energy?

Is there a limit, or can all energies below the maximum be produced? I realize that adding a filter could change the value for the minimum energy x-ray observed, but I mean without any filtration, could radio waves for instance be produced? Thanks for any help!

The spectrum should be continuous down to zero frequency, so that even radio waves are generated. However, when you look at the spectrum of a typical x-ray tube, you will see that the maximum of the continuous spectrum (below the characteristic lines) is not so far away from the highest possible energy, and that towards lower energies/longer wavelength, the intensity drops quickly. Add to that the exit window of the tube, which usally is Beryllium metal and you get a cut-off somewhere near 3 keV or so.

Synchrotron radiation from bending magnets is nothing than Bremsstrahlung from relativistic electrons. That spectrum goes from hard x-rays all the way down to visible and infrared.